1. Field of the Invention
The present invention relates to an external connector for a solid insulated load break switchgear, and particularly, to an external connector for a solid insulated load break switchgear capable of enhancing an insulting performance, and capable of connecting switches for three phases to one another with using connectors of the same shape.
2. Background of the Invention
A load break switchgear is an electrical apparatus used to diverge, test and maintain an undergrounded distribution line of a high voltage, and serves as distribution equipment of a high voltage of several tens of kilo volts (kV)˜several hundreds of kilo volts (kV). Generally, the load break switchgear includes a plurality of switches having movable contactors and fixed contactors according to phases of R, S and T of alternating currents, and a terminal part connected to the switches. Since the load break switchgear deals with a high voltage, each switchgear is mounted in a container where an insulating gas such as sulphur hexafluoride (SF6) is contained in a sealed state, the insulating gas having excellent arc-extinguishing and electric insulating performances.
Recently, it is required to remotely control the gas insulated load break switchgear so that the gas insulated load break switchgear may be open and closed in an automatic manner, for safety, rapidness in opening and closing operations, and reductions of a man power and costs. As relevant communications and motor control techniques develop, launched is a gas insulated load break switchgear having a control box installed therein, the control box having a communication function for automatic opening and closing in a remote manner, and having a motor actuator control function.
The control box obtains an operation power from a bus part of the load break switchgear, i.e., a line connected to an underground distribution line or a switchgear side. Since the control box is operated with a preset low direct current (DC), it is provided with a potential transformer installed therein so as to transform a high alternating current (AC) to a preset low DC.
The sulphur hexafluoride (SF6), one of gases regarded as a major cause of the global warming, is not used as an insulating gas for the switchgear. Rather, being developed is a solid insulated load break switchgear where the switchgear is electrically insulated by a solid insulating material.
FIGS. 1 and 2 are an exploded perspective view and an assembled sectional view, respectively showing an external connector for a solid insulated load breaker switchgear in accordance with the conventional art.
As shown, the conventional solid insulated load break switchgear (hereinafter, will be referred to as a switchgear) is disposed at an upper part of a receptor (not shown), and an external connector 1 for electrically connecting a plurality of switches (not shown) to each other is disposed at a lower part of the receptor.
To the switchgears for three phases, bushings 2 are electrically connected. Below the bushings 2, disposed are connectors 3 of the external connector 1.
The bushings 2 are disposed in a single line in a horizontal direction so that each receptor (not shown) may be provided with three bushings for three phases (e.g., receptor 1a is provided with R1, S1 and T1, receptor 1b is provided with R2, S2 and T2, receptor 1c is provided with R3, S3 and T3, and receptor 1d is provided with R4, S4 and T4).
The connectors 3 are disposed in a single line in a horizontal direction in correspondence to the bushings 2. And, the connectors 3 are formed of rubber having conductivity. A plurality of switches for three phases such as R, S and T are horizontally disposed, and bus parts 4 are integrally provided at each one side of the switches for implementation of three phases. The bus parts 4 for three phases are formed at right and left sides of the connectors 3 and at upper and lower sides of the connectors 3, so as not to overlap one another on a horizontal line.
In the conventional external connector 1, the bushing 2 having a bushing conductor 2a is coupled to an upper end of the connector 3, and a plug 5 for connecting the bushing conductor 2a to one end of a connection conductor 3a of the connector 3 is coupled to a lower end of the connector 3. A bus conductor 4a provided in the bus part 4 is connected to another end of the connection conductor 3a, thereby being electrically connected to the bushing conductor 2a by the connection conductor 3a. 
Unexplained reference numeral 3b indicates a bus connection part, 6 indicates a spring washer for elastically supporting the bushing conductor and the connection conductor, and 7 indicates a plug cap for prevention of introductions of foreign materials.
In the external connector of the conventional art, once an R phase is assembled, an S phase is assembled such that a bus part is toward a front side. Then, a T phase is assembled such that a bus part is toward a lower side in an opposite manner to the R phase.
However, the conventional solid insulated load break switchgear may have the following problems. Firstly, since the bus part 4 is formed to be slanted to one side of the connector 3, an electric field distributed on a connection surface where the bus part 4 is located (hereinafter, will be referred to as a first connection surface) 8a is asymmetrical to an electric field distributed on an opposite connection surface to the bus part 4 (hereinafter, will be referred to as a second connection surface) 8b. This may partially lower an insulating performance, and may cause dielectric breakdowns.